Baggage screening is conducted at all major airports today. It usually takes the form of an X-ray machine which allows the user to view the contents of carry-on baggage in order to detect any weapons or other contraband. While a metal pistol or knife is obvious and easy to see, explosive devices have gotten more sophisticated and hard to spot. Some devices have been disguised as electronic gear such as personal portable radios or tape players. Such a device is difficult to recognize and distinguish from a real radio or tape player, even for an experienced user.
A further problem is that the job of baggage screening can become repetitious, leading to lapses in attention during which potentially dangerous items may be inadvertently allowed on board an aircraft.
While it is possible to have someone periodically try to breach the baggage screening security, in time a single person would begin to be recognized by the users and they would increase their attention whenever that person came to their machine. Thus it would require more than one person, thereby raising its cost. Furthermore, if the users's performance were to be quantified, the costs and inconvenience would increase considerably.